[PATCH 5.10 047/406] security: keys: perform capable check only on privileged operations

Greg Kroah-Hartman
2023-09-17T19:23:06Z

From: Christian Göttsche <cgzones@googlemail.com>

[ Upstream commit 2d7f105edbb3b2be5ffa4d833abbf9b6965e9ce7 ]

If the current task fails the check for the queried capability via
`capable(CAP_SYS_ADMIN)` LSMs like SELinux generate a denial message.
Issuing such denial messages unnecessarily can lead to a policy author
granting more privileges to a subject than needed to silence them.

Reorder CAP_SYS_ADMIN checks after the check whether the operation is
actually privileged.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
security/keys/keyctl.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 61a614c21b9b6..e3ffaf5ad6394 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -980,14 +980,19 @@ long keyctl_chown_key(key_serial_t id, uid_t user, gid_t group)
ret = -EACCES;
down_write(&key->sem);

- if (!capable(CAP_SYS_ADMIN)) {
+ {
+ bool is_privileged_op = false;
+
/* only the sysadmin can chown a key to some other UID */
if (user != (uid_t) -1 && !uid_eq(key->uid, uid))
- goto error_put;
+ is_privileged_op = true;

/* only the sysadmin can set the key's GID to a group other
* than one of those that the current process subscribes to */
if (group != (gid_t) -1 && !gid_eq(gid, key->gid) && !in_group_p(gid))
+ is_privileged_op = true;
+
+ if (is_privileged_op && !capable(CAP_SYS_ADMIN))
goto error_put;
}

@@ -1088,7 +1093,7 @@ long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
down_write(&key->sem);

/* if we're not the sysadmin, we can only change a key that we own */
- if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid())) {
+ if (uid_eq(key->uid, current_fsuid()) || capable(CAP_SYS_ADMIN)) {
key->perm = perm;
notify_key(key, NOTIFY_KEY_SETATTR, 0);
ret = 0;
--
2.40.1